In forming corner stitches for, e.g., a mattress, the raw edges of a rectangular piece of quilted fabric are closed with an “overlock” sewing stitch, while applying a piece of “flange” material to the outer perimeter as the machine sews. The sewing machine has a small oscillating trim edge knife that sits just outside the needle sewing line, cutting a smooth edge for the stitch to lay over. When the operator reaches the corners of the rectangle, they actually turn a radius corner, trimming away the square corner as they sew. This radius ideally, matches the radius of downstream components, namely, the radius of the corner springs and the radius of the accompanying boarder wire, used in the final assembly of the mattress. Inconsistencies in the radius formed by the sewing machine operator (e.g., a 3.25 inch or 3.5 inch radius with a 3 inch ideal specification) cause production problems downstream that require an increase in the skill levels of other operators who need to assemble the final pieces of the mattress and correctly match up the corners and align the final pieces.
Other conventional approaches to obtaining consistent corner radiuses have employed automated sewing workstations that mechanically manipulate the sewing material throughout the entire sewing cycle, using combinations of conveyor feeds and corner turning devices, to form the side and corner stitches. The corner forming devices of these sewing workstations are based on an indexing driven circular plate. This plate drops down on the material, at a consistent location relative to the square edge corner (located by various edge sensors) and wrenches the material an angular increment, in time with the needles of the sewing machine. That is, when the needles come out of the sewing material after forming a stitch, the indexing driven circular plate turns “x” degrees, turning the material “x” degrees, as well as trimming away “x” degrees of the square corner). When the sewing material has completely formed a corner (as determined by an array of edge sensors), the indexing driven circular plate retracts, and a conveyor drive of the sewing workstation assumes control of the material, sewing down another long side of the material.
Disadvantageously, the aforementioned sewing workstations are problematic in that the associated mechanisms are inherently complicated and expensive. By the nature of the forces involved, these mechanisms are disproportionately large, fueling a spiral cycle of larger motors, larger motor mounting brackets, larger turning arms, and so forth. The end result is a big sewing workstation, which still requires a human being to feed it with material, and get it started. Further, such a sewing workstation is considerably more expensive than its manual counterpart, and requires a highly trained and adept engineer to be on staff to troubleshoot problems when they occur.
Accordingly, it would be desirable and highly advantageous to have a corner turning assist device for a sewing machine that overcomes the above described problems of the prior art.